Pressure regulating valves are used in myriad industrial and residential applications for controlling the downstream pressure of a fluid. For example, in chemical processing plants or oil refineries, pressure regulating valves are used to manipulate a flowing fluid to compensate for increases or decreases in demand, or other load disturbances, and thus keep the fluid pressure regulated. Similarly, pressure regulating valves may be used in plumbing fixtures to maintain a pre-determined pressure of fluid that automatically adjusts to variations in demand, such as anti-scald valves in showers or faucets. By controlling downstream pressure, pressure regulating valves compensate for variations in downstream demand. For example, as downstream demand increases, pressure regulating valves open to allow more fluid to flow through the pressure regulating valve, thus maintaining a relatively constant downstream pressure. On the other hand, as downstream demand decreases, pressure regulating valves close to reduce the amount of fluid flowing through the pressure regulating valve, again maintaining a relatively constant downstream pressure.
Pressure regulating valves can be categorized as either balanced or unbalanced. Unbalanced valves typically have high pressure inlet fluid on one side of the valve plug and lower pressure outlet fluid on the other side of the valve plug. Unbalanced valves suffer from an undesirable effect known as decaying inlet characteristic. The decaying inlet characteristic is a phenomenon in which an unbalanced valve experiences an unintended increase in downstream pressure as the upstream pressure decreases. This effect is undesirable as most pressure regulating valves attempt to maintain a constant downstream pressure. Decaying inlet characteristic is caused by fluid forces on the high pressure side of the valve plug attempting to move the valve plug to a closed position. As a result, the valve must have some mechanism to oppose this fluid force on the valve plug. Because the mechanism that opposes the fluid force typically has a set point, the force generated by such a mechanism is constant while the fluid force on the inlet side of the valve plug may vary (e.g., due to a decreasing supply of inlet fluid, or due to pressure variations upstream of the valve). Decaying inlet characteristic is particularly important to applications having a limited compressed fluid source, such as gas cylinders, tube trailers, or hydrils, because in such applications, there is a fixed supply of inlet fluid and thus, the inlet fluid pressure decreases as the inlet fluid supply decreases.
Unbalanced valves also suffer from damage that occurs to the valve seat. In unbalanced valves with high inlet pressures, the fluid pressure acting on large valve orifices can crush the valve seat. As a result, unbalanced valves are not ideal for high pressure, large orifice applications.
To address the decaying inlet characteristic in higher flow applications, balanced pressure regulators were developed. In the balanced pressure regulator, a portion of the upstream pressure is diverted to act on a downstream portion of the valve plug. Thus, the valve plug is “balanced,” having the same fluid pressure act on both upstream and downstream portions of the valve plug. In this way, the decaying inlet characteristic is eliminated (or greatly reduced) because there is no difference in the fluid forces acting on valve plug surfaces both upstream and downstream of the valve seat that would tend to force the valve plug towards the closed position. In other words, the valve plug itself generates very little, or no opening/closing forces due to fluid pressures.
In diaphragm-type pressure regulators, higher pressure fluid from an upstream or inlet side of the valve plug may be vented through the valve plug to an opposite side of the diaphragm to balance forces on the valve plug, similar to the balanced regulators described above. Typically, this balancing of fluid forces is accomplished by incorporating one or more vent channels or ports that extend through the valve plug from the inlet side to an actuator side of the diaphragm.
A typical diaphragm-type (balanced) pressure regulator valve is illustrated in FIG. 1. More specifically, FIG. 1 depicts one conventional gas regulator 10 comprising an actuator 12 and a balanced pressure regulator valve 14. The regulator valve 14 defines an inlet 16 for receiving gas from a gas distribution system, for example, and an outlet 18 for delivering gas to an end-user facility such as a factory, a restaurant, an apartment building, etc. having one or more appliances, for example. Additionally, the regulator valve 14 includes a valve seat 22 disposed between the inlet 16 and the outlet 18. Gas must pass through the valve seat 22 to travel between the inlet 16 and the outlet 18 of the regulator valve 14.
The actuator 12 is coupled to the regulator valve 14 to ensure that the pressure at the outlet 18 of the regulator valve 14, i.e., the outlet pressure, is in accordance with a desired outlet or control pressure. The actuator 12 is therefore in fluid communication with the regulator valve 14 via a valve mouth 34 and an actuator mouth 20. The actuator 12 includes a control assembly 22 for regulating the outlet pressure of the regulator valve 14 based on sensed outlet pressure. Specifically, the control assembly 22 includes a diaphragm 24, a piston 32, and a control arm 26 having a valve plug 28 with a valve disc 31. The diaphragm 24 senses the outlet pressure of the regulator valve 14 and provides a response to move the valve plug 28 to open and close the regulator valve 14. The control assembly 22 further includes a control spring 30 in engagement with a top-side of the control assembly 22 to offset the outlet pressure sensed by the diaphragm 24. Accordingly, the desired outlet pressure, which may also be referred to as the control pressure, is set by the selection of the control spring 30.
The diaphragm 24 is operably coupled to the control arm 26, and therefore, the valve plug 28, via the piston 32, and controls the opening of the regulator valve 14 based on the sensed outlet pressure. For example, when an end user operates an appliance, such as a furnace, for example, that places a demand on the gas distribution system downstream of the regulator 10, thereby decreasing the outlet pressure. Accordingly, the diaphragm 24 senses this decreased outlet pressure. This allows the control spring 30 to expand and move the piston 32 and the right-side of the control arm 26 downward, relative to the orientation of FIG. 1. This displacement of the control arm 26 moves the valve plug 28 away from the valve seat 22 to open the regulator valve 14, thereby increasing the outlet flow to meet the increased demand from the appliance and increasing the outlet pressure back to the control pressure. So configured, the appliance may draw gas through the valve seat 22 and through the outlet 18 of the regulator valve 14.
Referring now to FIG. 2, an enlarged cross-sectional view of the balanced regulator valve 14 of FIG. 1 is illustrated. In this example, the balanced regulator valve 14 further includes a body 19 having a passage 21 that fluidly connects the fluid inlet 16 with the fluid outlet 18. The passage 21 includes a throat 23 in which the valve seat 22 is disposed. A load spring 25 is connected to a valve stem 27 that is operatively attached to the valve plug 28. As explained, the valve disc 131 of the valve plug 28 interacts with the valve seat 22 to control fluid flow through the valve body 19 from the inlet 16 to the outlet 18. In addition, the valve plug 28 includes a circumferential recess 29 into which the valve disc 31, which is typically rubber, is disposed. The valve disc 31 of the valve plug 28 contacts the valve seat 22 to achieve alignment and sealing engagement between the valve plug 28 and the valve seat 22.
A diaphragm 33 is connected to the valve plug 28 and a plug housing or sleeve 35. The diaphragm 33 separates the passage 21 from a cavity 37 in the sleeve 35 that contains the load spring 25. The diaphragm 33 is responsive to pressure differences between the passage 21 and the cavity 37.
A retainer 39 may be operatively attached to the valve stem 27 and retains the valve plug 28 on the valve stem 27. The retainer 39 may include one or more fasteners 39a, such as a nut, which are attached to the valve stem 27. One or more balancing passages or channels 41 fluidly connect the passage 21 with a chamber 43 located between the valve plug 28 and the cavity 37. Fluid forces on the valve plug 28 are balanced by fluid moving through the balancing channels 41.
One problem with balanced pressure regulators, such as the balanced regulator 14 illustrated in FIG. 1, is that a contact seal between the valve disc 31 of the valve plug 28 and the valve seat 22 is affected by orientation and manufacturing tolerances between the disc 31 and valve seat 22. Such orientation and manufacturing tolerances often increase the amount of pressure required to make a seal, increasing lockup. For example, and as illustrated in FIG. 3A, due to normal part tolerances and assembly methods, for example, the valve disc 31 of the valve plug 28 often approaches the valve seat 22 in a non-parallel manner. When such a non-parallel approach occurs, a seal between the disc 31 of the valve plug 28 and the valve seat 22 is made on only one side of the valve seat 22, e.g., the left side, as illustrated in FIG. 3B. The other side of the valve seat 22, e.g., the right side, remains unsealed. As illustrated in FIG. 3C, when a complete seal is eventually achieved, one side of the valve disc 131 that initially contacts the valve seat 22 has a deeper indentation, resulting in a higher lockup or outlet pressure than desired and a less efficient regulator.